Conventionally, a gas sensor such as an A/F sensor or an O2 sensor is provided to the exhaust system of the engine. Since ceramic is generally used for the sensor element of the gas sensor, an element crack may occur when the sensor element is moistened at high temperatures. In this regard, in order to prevent the element from cracking due to element moistening, the gas sensor used for the exhaust system of the engine is generally equipped with a cover constructed to cover the sensor element and have ventilation characteristics.
The output of the gas sensor attached to the engine exhaust system such as the A/F sensor or O2 sensor is used for an air/fuel ratio control, for example. Now, as an approach to environment problems, the importance of which is rising, and early activation of the sensor element is strongly required to reduce exhaust emissions. In order to achieve the early activation of the sensor element, the gas sensor may be equipped with a heater, which raises the temperature of the sensor element.
For example, there are arts that are intended to prevent element cracking due to element moistening and may be relative to the present invention. Patent Documents 1 and 2 propose arts that may relate to the present invention in terms of a predetermined heater control taking condensed water into consideration. Patent Documents 3 and 4 propose arts that may relate to the present invention in terms of arts associated with the start timing of a predetermined heater control. Patent Document 5 discloses an art that may relate to the present invention in terms of arts taking dew condensing conditions into account.